This invention relates to underground access conduit for accessing an underground valve or other underground mechanism from an aboveground position, and more particularly, to the adaptation or extension of the access conduit to grade level.
Municipal utility companies usually supply their services, such as gas and water, to their customers via underground pipes. Flow control valves are placed along the pipes to control the supply to individual customers. It is not uncommon that the control valves that supply individual customers be located under ground at the curb of an adjacent roadway.
For example, in a municipal water system, the source of water is the water main that runs beneath the street. A valve, referred to as a curb stop, is located at the property line between the main and the customer inlet water pipe to control the flow of water to the customer. The curb stop is used to shut off the water for repairs, nonpayment of water bills, flooded basements, and the like. The curb stop is used as the isolation valve. The curb stop is accessed from aboveground through a conduit known by many names, such as valve can, valve box, or curb box, that extends from the valve to ground level, providing a conduit for inserting a long-handled wrench or xe2x80x9ckeyxe2x80x9d used to reach the valve.
FIGS. 1-2 illustrate a common type of curb box 2 currently in use. The curb box 2 comprises a generally tubular casing 10 having an enlarged lower bell housing 12 that is adapted to cover at least a portion of the valve 6 containing the control knob 4. The upper end of the curb box 2 generally includes a cover 30 which is commonly flush with grade level 8. The cover 30 is coupled to the casing 10 via a box top 20 which is used to reinforce the surface end 14 of the casing 10. The box top 20 provides a lower end 22 adapted such that the surface end 14 is slidably received into the lower end 22. The box top 20 provides an upper end 24 adapted to couple with the cover 30.
Typically, an elongated wrench is used to reach down into the curb box 2 to turn the valve operating knob 4, which is often referred to as a valve head. The location of the valve 6 below grade can vary depending on many considerations, including the freeze level and the mains depth. For example, the depth of the mains can be between 1 to 4 meters (3-12 ft.) below grade level 8.
The curb box 2 is initially installed in the same open trench prepared for the pipes and associated valve 6. The curb box 2 is placed over the valve 6 and held perpendicular to grade level. The trench is back-filled surrounding the curb box 2 with backfill material. During the back-filling procedure, the curb box 2 is properly located with respect to the valve 6 and, even though the back-filling may be performed using bulldozers, back hoes or other power equipment, the curb box 2 must stay positioned on the valve 6 even though subjected to lateral forces and pressures while being surrounded by backfill material.
During initial installation of the curb box 2, and prior to back-filling the trench, there are number of methods used to establish the proper length of the curb box 2 such that it is flush with grade level 8 while properly containing the valve 6. One method is to cut the casing 10 at the surface end 14 to the proper length. This method is relatively straight-forward for installations wherein the casing 10 is relatively short in length and that the cutting is made prior to placement over the valve 6. It does require some skill in making the correct cut in length on the first attempt.
For installations requiring the casing 10 to be longer, it is not uncommon that the casing 10 be comprised of two or more sections: a lower bell section 10a and one or more upper extension sections 10b which are coupled together using mechanical coupling devices 11, such as with a band clamp and the like, as shown in FIG. 3. The bell section 10a includes the bell housing 12 at a lower end 16 and a tubular portion 13 at an upper end 15. The one or more upper extension sections 10b comprise a tubular member having a predetermined length and having a uniform diameter of the same size as the diameter of the upper end 13. One end of the upper extension section 10b is coupled to either another upper extension section 10b or the upper end 13 of the bell section 10a. 
The adjacent ends of any two sections 10a, 10b are commonly butt joined and held together with any number of coupling devices 11, such as a screw-driven band clamp, or a bolted or threaded union coupling. Assembly of the sections either outside of the trench or within the trench is relatively straight-forward but time consuming. The mechanical coupling devices 11 require proper assembly to hold and retain the joining sections 10a, 10b in coaxial alignment, a time consuming process requiring centering, alignment, shifting and adjustments.
It is not uncommon that during the service life of the curb stop 6, there is a need for the curb box 10 to accommodate for elevation change of grade level 8, either upwards or downwards. This might be due, for example, to the addition of pavement in a street installation or to a change in landscaping.
For example, during roadway resurfacing, a layer of paving material is caused to become disposed over the existing pavement, resulting in the curb box cover 30 being below the grade level 8 of the new pavement and thereby causing a depression in the roadway. It becomes necessary to either replace the existing curb box 10 with one of the proper length or disassemble a multi-section curb box 2 and reinstall a longer upper extension section 10b. 
The method to replace or disassemble the curb box 2 is usually to excavate the area above the casing 10, provide some method of retention of the unexcavated material, and have repair personnel enter the excavation to facilitate the replacement or reassembly of the casing 10 with one of proper length. The process of excavation to gain access to the curb box 2 or the coupling device 11 involves the use of heavy excavation equipment risking damage to the curb box 2. Further, the coupling device 11 might be inoperable due to corrosion making removal difficult.
Apparatus and methods for the adjustment of the height of the curb box 2 that is completed from above grade level with a minimum of excavation would be advantageous in terms of time, labor and equipment costs while minimizing the potential for damage to the curb box 2.
The present invention comprises a valve can extension for use as a component of a valve can, otherwise known as a curb box or valve box. The valve can is used between an underground valve and the ground surface providing a conduit such that the valve handle may be turned from aboveground using an elongated key. The valve can extension comprises a tubular column having an extension riser portion at one end and an inwardly tapered portion at the other end. The extension riser portion has a substantially constant inner and outer diameter defining a substantially uniform wall thickness. The inwardly tapered portion is adapted to be inserted into and frictionally engage a valve can bell housing forming a valve can having a substantially uniform inner and outer diameter from above the bell portion of the bell housing to grade level. The valve can extension provides the ability to establish the elevation of the valve can with regards to grade level. A simple joining method is provided to negate the need for complex mechanical coupling devices. The valve can extension further provides the ability to change the elevation of the valve can without the necessity of major excavation and back-filling to gain access to and rebury the coupling between the valve can extension and the bell housing.